Core box

ABSTRACT

A CORE BOX FORMED OF A UREA-FORMALDEHYDE-GAMMA AMINO PROPYL TRIETHOXY SILANE-FURFURYL ALCOHOL THERMOSETTING RESIN WHICH IS SUBSTANTIALLY LOSSLESS TO MICROWAVE ENERGY COATED WITH A COATING WHICH IS LOSSLESS TO MICROWAVE ENERGY, SUCH AS POLYETHYLENE, POLYPROPYLENE, OR POLYURETHANE.

United States Patent Oihce 3,814,626 Patented June 4, 1974 US. Cl. 117-138.8 A 1 Claim ABSTRACT OF THE DISCLOSURE A core box formed of a urea-formaldehyde-gamma amino propyl triethoxy silane-furfuryl alcohol thermosetting resin which is substantially lossless to microwave energy coated with a coating which is lossless to microwave energy, such as polyethylene, polypropylene, or polyurethane.

- This is a division of application Ser. No. 35,902, filed May 8, 1970, now Pat. No. 3,692,085.

BACKGROUND OF THE INVENTION Field of the invention "This invention relates to a process for producing cores within a core box wherein the core is cured by the application of microwave energy.

Description of the prior art One of the major problems of foundry work is providing molds for the articles being cast. The most economical wayto provide these molds is to make the mold of as cheap of a material as possible which can withstand the heat of the molten metal for a period of time long enough for the molten metal to solidify. After the cast metal has solidified the cast article is removed by the mold being opened. Such structural molds are also necessary when a hollow object is being cast in which the cross-sectional area at some point in the hollow part is greater than the cross-sectional area at the entrance of the hollow part. It is obvious that in these applications, it is almost necessary to break the core and remove the pieces of the core through the smaller cross-section openings.

. The most widely used material for constructing molds and cores in the foundry industry is sand to which has been added a suitable binder material to cause the mold orcore to retain its shape until the material has been poured and solidified. When sand is used in a foundry, the core and mold are formed by a suitable process and the core is placed within the mold and molten metal is pou'redinto the mold. After the metal solidifies the outer mold-is broken off and the metal object is usually vibrated to break up the sand so that the sand may be poured out of the openings of the hollow cast object. The sand from the mold and core can then be recovered and reused.

'The sand mold is traditionally made from damp sand packed around a model of the object to be cast. The mold is usually made in two halves with the halves being presed around the opposite halves of the model thereby forming a two piece hollow mold the inner surface of which reproduces the outer surface of the object to be cast.

One of the early ways of making suitable cores was to form a two piece mold the inner surface of which conformed to the outer surface of the core which was de sired to be made. Sand mixed with a cereal binder was then pressed or rammed into the mold. The cereal binder held the sand together so that the sand mixture would retain its shape when removed from the mold and then further cured. Such a mold in which a core is made is knownjin the art as a core box. The core boxes for this application were normally wooden boxes.

The next advance in the foundry art was the so-called no-bake resins where the sand was mixed with a binder and catalyst and then placed in a woden box. The catalyst partially cured the core so the core box could be removed and the core then cured to the final desired state.

The next advance in this art was the introduction of the so-called hot box process. In this method, the sandbinder-catalyst mixture was blown by a core blower into a heated steel or iron box. The heated box cured the outside or skin of the core and the core was then removed and allowed to cure on standing. Core boxes for this process were normally made of iron or steel and were made by hand by skilled die makers.

The present process is an advancement over all these prior art methods.

One of the more recent prior art methods for producing cores is explained in US. Pat. 3,429,359. This method is one in which a core is formed within a core box that is transparent to microwave energy, and the core box is permanently and immovably supported in a microwave heating cavity and the core cured by the application of microwave energy. This process, however, has one serious deficiency in that it teaches only the use of a static, nonmoving microwave system. While the system is good in theory, it is not an effective practical method for producing core boxes. The uneven curing produced by the method does not fulfill the needs of the foundry industry. The present invention has overcome these problems asso ciated with the prior art.

SUMMARY OF THE INVENTION It is an object of this invention to provide a process for producing cores.

It is another object of this invention to provide a process for producing cores wherein the cores have uniform curing.

It is another object of this invention to provide a system for producing cores.

It is still another object of this invention to provide a process for producing core boxes.

It is still a further object of this invention to provide a new and novel core box.

The objects of this invention are accomplished by a process for producing cores which comprises the steps of forming a core box from a thermosetting resin, preferably coating the interior surface of the core box with a release agent, inserting a lossy core forming material into said core box, and applying microwave energy to said core box in a manner which substantially eliminates standing microwaves in said core box.

More particularly the new process of this invention is one which comprises the steps of forming a core box from a material which is lossless to microwave energy, blowing a lossy core forming material into said core box, and applying microwave energy to said core box in a man ner which substantially eliminates standing microwaves in said core box.

The objects of this invention are further achieved by an improvement in the combination of a core box made from a material which is transparent to microwave energy, a microwave heating cavity, means for supporting said core box in said cavity, means for blowing a core forming material into said core box, and means for applying microwave energy to said cavity, wherein the improvement comprises means for eliminating standing microwave in said core box.

In one preferred embodiment of this invention, a core box is formed from a thermosetting resin which is lossless to microwave energy and the core box is then coated with a material which is lossless to microwave energy. This invention includes the coated core box and the method of producing it.

The heart of this new invention lies in the fact that the application of microwave energy to a core box must be in a manner which substantially eliminates standing microwaves in the core box. When microwave energy is introduced in a processing enclosure, some of the microwaves are reflected from the walls of the enclosure. These reflected microwaves reenforce each other in some locations in the enclosure and cancel each other out in other locations in the enclosure. When an object is being heated in the enclosure, the reenforced waves cause hot spots, and the wave-cancelled locations cause cold spots in the object. By the term standing microwaves it is therefore intended to mean reflected microwaves which reenforce and cancel each other out causing hot and cold spots in the object to be heated.

One method of eliminating standing microwaves in a core box is to design the enclosure and the core box so that the microwaves will not substantially reenforce or cancel each other. This presents some design problem, however, and is thus not the preferred practice in foundry operations.

The preferred method of eliminating standing microwaves in the core box is to apply the microwave energy to the core box as the core box moves through or past the microwave energy source. One method of accomplishing this is to have the core box travel on a conveyor through a microwave oven. The heating accomplished by this process is a result of many different combinations of reenforced and canceled microwaves, the sum total of which results in even heating and curing of the core in the core box.

By use of the term thermosetting resin it is intended to mean generally a resin which sets or polymerizes upon heating. Of particular importance to this invention are polyurethanes of the non-elastomeric type which are also lossless to microwave energy. Also of importance in this invention are furfuryl alcohol resins or furan resins consisting of polymerized furfuryl alcohol. In these resins, further polymerization to a solid from the normally liquid resin can be accomplished by the addition of a catalyst. When the furan resins are used as core binders in microwave applications, the resin may contain a lossy material such as urea. When the resins are used as binder for the core box, an essentially un-modified furfuryl alcohol resin can be used since the cured resin must be substantially transparent to microwave energy. At this point, it is important to note that furfuryl alcohol monomer and slightly polymerized furfuryl alcohol are lossy to microwaves while substantially polymerized furfuryl alcohol is substantially lossless to microwaves. As a furfuryl alcohol monomer is cured to form a polymer, it necessarily changes from a lossy material to a lossless material. Also of particular importance for use in this invention are the phenolic resins consisting of phenol and some other material such as formaldehyde and providing that the combination is lossy to microwave energy when the resin is used as a core binder and providing that the resin is lossless to microwave energy when it is used as a binder for the core box.

Of special importance as a preferred embodiment of this invention is a foundry core composition prepared by the process comprising the steps of:

(a) forming a monomeric binder mixture of from 2% to 10% by weight of aqueous urea formaldehyde mixture, from 0.0125 to 0.5% by weight gamma amino propyl triethoxy silane, and from 89.5% to 97.9875% by weight furfuryl alcohol, said aqueous urea formaldehyde mixture containing from about to about 25% by weight water;

(b) forming a mixture of from 3700 to 3979 parts by weight sand and from 1 to 100 parts by weight acidic catalyst; and

(c) admixing from /2% to 5% by weight of the monomeric binder with from 95% to 99.5% by weight of the sand-acidic catalyst mixture.

The definition of the terms urea formaldehyde mixture and acidic catalyst and other procedure may be taken to be the same as is defined in US. Pat. No. 3,168,489 to Lloyd H. Brown et al. issued on Feb. 2, 1965, with the notable difference in the stated amount of water in the urea-formaldehyde mixture.

One embodiment of this invention is the process for producing cores which comprises the steps of forming a core box from a thermosetting resin, coating the interior surface of said core box with a material which is lossless to microwave energy, inserting a lossy core forming material into said core box, and applying microwave energy to said core box in a manner which substantially eliminates standing microwaves in said core box. The forming of the core box from a thermosetting resin is accomplished by methods well known to the art. The resinsused in forming the core box comprise the hereinbefore mentioned furfuryl alcohol resins or furan resins, phenolic resins, polyurethanes and mixtures thereof. It is preferred to coat the interior surface of the core box with a material which will decrease the bonding between the resin inthe core mix and the core box. Any suitable material may be used for coating the, interior surface of the core box as long as the material has properties which allow it to be applied in a coating form. The coating material or release agent can be substantially lossless to microwave energy; It is to be understood, however, that in some applications it may be desired to provide a quicker cure or higher degreeof cure at the surface of the core in which case a lossy material should be added to the coating material to achieve the desired result. Among the substantially lossless materials that may be used for coating the interior surface of the core box are the various polymers such as polyethylene, polypropylene, and polyurethane either alone or in some type of solution. Other plastic materials which are lossless to microwave energy should be equally acceptable for this coating procedure. The lossy core forming material that is then inserted into the core box comprises one of the aforementioned furfuryl alcohol or furan resins, phenolic resins, or polyurethanes each of which has had added thereto a lossy material. When phenolic resins are used as the core binder, formaldehyde is the most frequently preferred lossy material to be added to the resin. These lossy materials are not the only ones that are operable, however, and other well known lossy materials common to the microwave art such as ferrite materials or carbon may also be added to the resins to impart a lossy nature to them. The resin with the lossy material therein is then cured by the application of microwave energy to the core box in a manner which substantially eliminates standing micro-waves in the core box. I

This invention also includes a process for making cores which comprises the steps of forming a core box from a material which is lossless to microwave energy, blowing a lossy core forming material into the core box and applying microwave energy to the core box in a manner which substantially eliminates standing microwaves in the .core box. Once more it is emphasized that the elimination of standing microwaves in the core box is an achievement which the prior art has never obtained in the foundryart.

The prior art has disclosed a core box made from a material which is transparent to microwave energy, a microwave heating cavity, means for supportingzthe core box in the cavity, means for blowing a core forming material into the core box, and means for applying microwave energy to the cavity. This invention, however, in cludes the improvement in the above described prior art wherein the improvement comprises the addition of means for eliminating standing microwaves in the core box. The preferred embodiment of this improvement is one in which the means for blowing a core forming material into .the core box is a means for blowing a mixture of sand and a thermosetting resin into the core box wherein the thermosetting resin is the same as has previously been described.

--This invention also includes a new and novel core box pomprising a formed thermosetting resin coated with a material which is lossless to microwave energy wherein saidthermosetting resin is also substantially lossless to microwave energy. The formed thermosetting resin for this core box is the same as has hereinbefore been described with care being taken to insure that no material is included which is lossy to microwave energy. Likewise, the coating materials that are herein used are those which have 'hereinbefore been described such as polyethylene, 'pt lypropylene, polyurethane, etc.

l The new process for producing these core boxes comprises the steps of forming a core box from a thermosetting resin which is lossless to microwave energy and then coating the core box with a material which is substantially lossless to microwave energy. Again the terms used herein are those which have hereinbefore been described.

DESCRIPTION OF THE PREFERRED Y EMBODIMENTS The following examples may be taken to constitute preferred embodiments of this invention.

Example 1 A sand mix was prepared by thoroughly admixing 90 weight percent sand, Weight percent silica flour and 10 weight percent clay. Ten weight percent (based on sand weight) of a no-bake furan resin (greater than 50% by weight furfuryl alcohol, Steelset trademark, Aristo Corp.International Minerals & Chemical Corp.) was then mixed with the sand mix and weight percent (based on resin weight) of concentrated phosphoric acid was then added and mixed therein. A wooden model was prepared and placed in a wooden mold. Both the model and'mold were coated with coating material comprising about 53.5 percent water, 3.5 percent Western bentonite, 24 percent graphite, 6 percent sodium soap of coconut oil, and 13 percent methanol. The sand-resin mixture was then packed lightly around the coated model in the mold. The wooden mold was used to hold the sand-resin mixture until the resin cured. A thin plastic sheet (a polyethylene terephthalate, Mylar, E. I. du Pont de Nemours & Co., Wilmington, Del.) was fastened to the mold to divide the mold into two parts at the core cavity. After the resin was cured, the plastic sheet was unfastened from the mold and the core box removed from the mold. The box was easily split at the plastic sheet and the core model removed. Since vents were not molded into the core box, they were then drilled in the box. The core cavity was then coated with a thin film of polyurethane, A sand mix consisting of about 50 weight percent reclaimed sand (containing about 1.7 Weight percent carbonaceous material) and 50 weight percent foundry sand were mixed with 2 weight percent (based on total sand weight) of a furan hot box binder (furfuryl alcohol resin, Sanset 22, trade mark, Aristo Corp.-International Minerals & Chemical Corp.) catalyzed with weight percent aqueous ammonium chloride: urea catalyst (Sanset 2, trademark of Aristo Corp.-International Minerals & Chemical Corp.). After the sand, resin, and catalyst were thoroughly mixed, the mixture was blown into the core cavity. The sand core box containing the uncured core was then passed into a microwave cavity on a conveyor belt and exposed to 3000 watts of microwave power at 2450 megacycles per second for 30 seconds. The core box was kept moving at approximately the same speed during its entire 30 second exposure in the microwave cavity. After the exposure period, the core box was moved out of the microwave cavity and after 3 minutes at room conditions, the core was stripped from the core box. The core was found to exhibit properties superior to any produced by prior microwave treatments.

Example 2.

' Example 1 was repeated except the no-bake furan resin comprised--92 parts by weight'furfuryl alcohol,-8 parts by weight urea-formaldehyde concentrate, :and 0.1

part by weight gamma amino propyl. triethoxy;silane. This core was-also found toexhibit properties superior ,to any producedby prior microwave treatments. Y

' Ex b A quantity of silica sand was weighed and set aside. A quantity of no-bake furan resin (greater than 50 weight percent furfuryl alcohol, Steelset trademark, Aristo Corp.International Minerals & Chemical Corp.) equal to 12.5 percent by weight based on the weight of the sand was then weighed and set aside. Next, 15 weight percent (based on furan resin weight) of a 70% solution of para toluene snlfonic acid in water was thoroughly mixed with the sand. The furan resin was then thoroughly mixed with the sand-catalyst mixture. After thorough mixing, the sand-resin-catalyst mixture was packed in a polyethylene mold around a polypropylene model of the core. The mold containing the uncored sand-resin-catalyst mixture was then passed into a microwave cavity on a conveyor belt and exposed to 3000 watts of microwave power at 2450 megacycles per second for seconds. The mold and its contents were kept moving at approximately the same speed during the entire 90 second exposure. After removal from the microwave cavity, the mold was allowed to set at room conditions for 3 minutes and the core box was then removed from the mold and the core model removed from the core cavity. The core was then brushed with a solution of water-bentonite-graphitesoap-methanol (same as in Example 1). Vent holes were then drilled in the core box to permit use of a conventional core blower to blow the core mix into the core cavity. Enough sand to fill the core cavity was then weighed and mixed with 2 weight percent (based on sand weight) of a no-bake furan resin (furfuryl alcohol) and 20 weight percent (based on resin weight) of concentrated phosphoric acid, the acid being mixed with the sand first and then followed by the resin. The core mix was then blown into the core cavity and the core box containing the uncured core mix was passed into the microwave cavity and exposed to 3000 watts of microwave power at 2450 megacycles per second for 30 seconds. The core box. Again, the core was found to exhibit excellent proximately the same speed during the 30 second exposure. After the core box was removed from the microwave cavity, the core was immediately stripped from the core box. Again, the core was found to exhibit excellent properties.

Example 4 A quantity of foundry sand was weighed and set aside. An amount of greater than 90% furfuryl alcohol containing no-bake resin equal to 15 percent by weight of the sand was then weighed and set aside. A solution of sulphuric acid (50% sulphuric acid in water) equal to 10 percent by weight of the furan resin was then mixed with the sand,

and the resin binder was then mixed with the sand and catalyst. After thorough mixing, the sand-resin-catalyfst mixture was packed in a metal mold which had been coated with the 'water-bentonite-graphite-soap-methanol mixture described in Example 1. The mold contained a wooden core model also coated with the same mixture. The mixture was allowed to cure and after curing the core box was removed from the mold and the core model removed from the core cavity. Vent holes were drilled in the core box to permit use on a conventional core blowing machine. The core cavity surface was then coated with silicone release agent. Enough sand to fill the core cavity was then weighed and to it was added about 1 percent by weight powdered graphite. Two percent (based on sand weight) of a phenolic resin binder (Sanset 33, trademark, Aristo Corp.International Minerals & Chemicals Corp.) and aye'cavity, it was allowed to set for about 3 minutes at 386m conditions,'and thecore was then stripped from the eoreboxk v In each of the above examples, the boxes were able to be subjected to at least 100 core blowing-core forming sequences without exhibiting a wear of over 0.005 inch. This 'posure-Afte'r'the core boxwas removed from the microwas superior to anything produced by prior microwave art.

Having fully described this new and novel invention, we claim:

1. A core box comprising a formed thermosetting resin coated with a material which is lossless to microwave energy, said thermosetting resin being substantially lossless to microwave energy, and said thermosetting resin comprising an acid curable urea-formaldehyde-gamma amino propyl triethoxy silane-furfuryl alcohol mixture, said material which is lossless to microwave energy comprising a polymer selected from the group comprising polyethylene, polypropylene, and polyurethanes, and said thermosetting resin comprising from 2 percent to 10 percent by weight aqueous ureaformaldehyde mixture, from 0.0" pereent to 0.5 percent gamma-amino trietho xy'silane, and from 89.5 percent to 97.9875 percent by weight'fur f ural "alcohol with from about 5 percenttojabout '25 "per'centjb'y weight water. v 1 References Cited v,

UNITED STATES PATENTS v Hugger "'.164I4 2,629,907 3/1953 2,763,757 9/1956 Pritchard 219'l1'0.55 3,168,489 2/1965 Brown et a1; :'26()-,12,1 3,189,722 6/1965 Fritz 219'-;10.55 3,201,498 8/1965 Brunson et al. l17--138,8 3,259,947 7/1966 Knight 1644 3 3,429,359 2/ 1969 Hollingsworth =164-37 3,519,517 7/1970 Dench 156-380 3,558,564 1/1971 Vasta 1.17.,161 3,578,552 5/1971 Prevorsek et a1 161-190 OTHER REFERENCES The International Dictionary of Physics and Electronics, D. Van Nostrand Company, Inc, 1956, p. 986.

WILLIAM D. MARTIN, Primary Examiner" S. L. CHILDS, Assistant Examiner s. 01. ,X.R.

117- 5.2, 138.8 D, 138.8 E, 161 KP; 161-190, 

